The present invention relates to a computerized manufacturing process. More specifically, the present invention relates to a computerized method that enables work pieces, e.g., parts of a shoe upper, to be accurately sewn together or to be sewn with decorative stitching lines, in a vision-aided, computer-guided process.
Traditional shoemaking techniques use a last, which is a solid form, over which a shoe will be made. The last looks somewhat like a foot, but without the toes and other such detail. Traditionally, lasts are hand crafted out of wood by a last xe2x80x9cmodel makerxe2x80x9d and then duplicated in volume, including grading for different sizes, on a special lathe, set up specifically for cutting lasts. A different size last (actually a pair of lasts, one for each foot) is needed for each size of shoe. Thus, a line of shoes that is available in half sizes 5-12 and widths narrow, medium, wide for each size, would require 45 pairs of lasts.
From each last, a shoemaker derives a set of paper patterns for each style of shoe to be made. One traditional way of deriving the paper patters is to cover the model size of a last (e.g., a size 9, medium last for men) with narrow (e.g., xc2xdxe2x80x3 wide) strips of tape. Once the last surface is completely covered with tape, the shoemaker would then sketch the shoe on the taped surface, showing all details of the shoe. The tape can then be peeled from the last surface in two halves by first cutting down the centerline of the last (toe to heel) and then laying it flat on a flat surface. The two halves are xe2x80x9cjoinedxe2x80x9d along their centerlines in the forefoot area.
This flattened tape is called a flattening and is a mechanical way of taking the 3-D surface of the last and translating it to a 2-D surface. The lines of the shoe on the 3-D surface are also shown on this flattening. From these lines, the shoemaker is able to layout all the patterns of the pieces to be cut (from leather and other materials) which will later be sewn together to make up the upper of the shoe. Typically the shoemaker cuts the pieces out of a heavy paper, thus making a set of paper patterns.
Paper patterns not only show the outline of the pieces to be cut, but all the details necessary to aid in production. This includes any perforations (eyelet holes, for example) or markers. A marker is a slot cut in a paper pattern to indicate the position of lines for stitching or guidance in placement of one part on top of another. From the finished set of paper patterns (including all sizes), a shoemaker can make the necessary cutting dies (normally made from band steel) and other templates and tools needed for production.
This shoemaking process has been in use pretty much unchanged since the beginning of the last century. Only in the past two decades have there been significant efforts and advances in some of these processes. For one, with the advent of computer driven CAD/CAM systems specific to the footwear industry, much of the pattern work is now done by computer instead of by hand. Paper patterns output from computer CAD/CAM systems can be plotted or cut on computer-guided tables, and these patterns used as guides for making steel cutting dies and the other templates and tools necessary for production.
Another area where progress has been made is through the use of computer-guided sewing machines. For example, computerized stitching or sewing machines can be employed to sew various pieces of a shoe together. Some computerized stitching machines perform sewing operations along a predetermined path using a sewing program stored in a computer-readable medium. A major drawback to most of these machines is that they are blind, i.e., they cannot see the work piece being sewn. Leather and textiles, basic work pieces in the manufacture of shoes, are flexible materials that may change size and position before and during the sewing process. Thus, occasionally the predetermined sewing path does not match the actual path being sewn resulting in pieces that are subsequently rejected during quality control inspections.
In order to overcome these deficiencies, companies have developed computerized sewing machines with xe2x80x9cmachine visionxe2x80x9d that detects the edges of the work piece being sewn. Machine vision includes the use of cameras and illuminating lights to detect and enhance the detection respectively of the edge of a work piece. With the edge of the work piece identified, the computer controller within the sewing machine can adjust the sewing path as necessary to compensate for misplacement or movement of the work piece or other variations that may otherwise lead to an erroneous sewing path. Edge detection is a complicated process, however, and slight variations in the lighting conditions, work piece characteristics (e.g., color of the leather) or other factors may cause the edge detection software to not function properly. Thus, set up time for an edge detecting machine vision sewing system is lengthy and changes in the work environment may require subsequent adjustments to the machine set up.
The traditional shoe manufacturing techniques described above are well suited for mass production, where long and tedious set-up procedures can be spread out over large production runs for large quantities of shoes with a limited number of sizes. They are not so well suited for the manufacture of custom shoes, where production can be done on a pair-by-pair basis, or at least for much smaller quantities than found in normal mass production. Typically, custom shoes are handmade, relying on skilled artisans and taking several weeks or more to manufacture.
Accordingly, improved shoe manufacturing techniques and equipment are desirable as is an improved method of manufacturing custom shoes.
Embodiments of the present invention provide improved shoe manufacturing techniques including a new method of operating a computerized, vision-aided sewing apparatus. The invention can be used to stitch one work piece to another or for stitching a decorative stitch line along a work piece.
In one embodiment, the method includes arranging a stencil over at least a portion of a work piece to be stitched. The stencil is cut from a material having a color selected to contrast with a color of the work piece. Next, a computer-controlled sewing apparatus having a machine-vision capability is used to stitch along a path that corresponds generally to an outer edge of the stencil. The computer-controlled sewing apparatus can adjust its stitching path in response to detecting the stencil. Then, after stitching is completed, the stencil is removed from the work piece.
In another embodiment, where a first work piece is stitched to a second work piece, the method includes arranging the first work piece so at least a portion of the piece overlies at least a portion of the second work piece and arranging a stencil over either the first or second work piece. The stencil is made from a material having a color that contrasts with a color of the first work piece. Next, the first work piece is stitched to the second work piece using a computer-controlled sewing apparatus having a machine-vision system. The machine-vision system facilitates stitching along or with reference to a stitching path that corresponds generally to an outer edge of the stencil and enables the sewing apparatus to adjust the sewing path in response to detecting the stencil. After stitching is completed, the stencil is removed.
In some embodiments, the machine-vision system for the stitching machine includes ultraviolet lamps to better illuminate the boundaries between the stencil and the work pieces.
Some embodiments of the invention are particularly useful for the manufacture of custom shoes, where many sizes of a given style of shoe (hundreds or even thousands of sizes), in production-run quantities as few as one half pair per size, can be stitched on a vision-aided computer stitching machine, with a minimum of set-up work required. Patterns output from a CAD/CAM system can include corresponding data to (i) cut and plot alignment lines on pallets used in the assembly of the shoes, (ii) cut the work pieces (shoe parts) to be stitched, (iii) cut the stencils used to guide the computer-controlled, machine-vision sewing system, and (iv) provide stitch line data for the stitching system.
These embodiments and others are described more fully in the Detailed Description below in conjunction with the following figures.